1. Field of the Invention
The invention relates to a liquid gas engine. Liquid gas engines are spark ignition Otto engines which are supplied with liquid gas.
2. Description of the Related Art
The main components of liquid gas, which is a mixture also designated as LPG (Liquefied Petroleum Gas), are propane and butane. It is obtained during the extraction of crude oil and in refinery processes and can be liquefied under pressure. Liquid gas is distinguished by a high octane number (RON&gt;100).
Liquid gas engines differ from gasoline engines in the different mixture preparation which is necessitated by the great tendency of liquid gas to evaporate. Liquid gas is supplied, as a liquid under pressure, to the engine in corresponding delivery lines. In an evaporator, the liquid gas is converted into the gaseous state by the supply of heat. The evaporator is a heat exchanger, to which heated cooling water is supplied in order to heat and evaporate the liquid gas. The evaporator is combined with a pressure regulator, in order to keep the then gaseous liquid gas within a specific pressure range. The liquid gas is then supplied to a gas/air mixer which mixes liquid gas with air. Such a gas/air mixture is known, for example, from DE 33 32 923 C2. The mixer consists of an annular element which supplies liquid gas from outside to a central air stream passing through the annular element and which swirls them together.
The company DAF presented a liquid gas engine for buses under the type designation LT 160 LPG. This liquid gas engine corresponds to a diesel engine which is converted to a liquid gas engine. In contrast to the known liquid gas engines, the engine presented by DAF is equipped with a liquid gas injection system which injects liquid gas into an intake port. This injection system corresponds entirely to those employed at the present time in Otto engines (passenger vehicles). When the liquid gas is being injected into the intake port, the mixture temperature is to be reduced, and higher efficiency established, as a result of the evaporation of the liquid gas. This cooling by evaporation may lead to the icing up of the injection valves in the starting phase and in the case of high air humidity, and, because of this, it is not possible to ensure that the engine will operate at cold outside temperatures. This could be counteracted by mixture preparation with simultaneous heating, as is known from the already conventional liquid gas engines. However, heating an ignitable mixture entails considerable risks.
Known from FR-A-2 629 516 is an internal combustion engine which is intended for the use of a fuel with a higher vapor pressure and significantly lower viscosity than gas oil. The engine works in accordance with the diesel process, and comprises a device for direct injection of the fuel under high pressure into the combustion chambers via passive mechanical injection nozzles, the device having a low-pressure feed pump, which is capable of regulating the pressure of a fuel to a value which suffices for the fuel not to reach the boiling point of 8000, and a high-pressure pump which is arranged in the vicinity of the injection nozzles. The high-pressure pump has a cylinder and a piston with smooth surfaces for relative displacement and sealing, the surfaces being separated from one another by a radial play of the order of magnitude of 1 .mu.m, and the piston having open surface pores which are impregnated with a lubricant which is resistant to friction and the effect of the fuel.
This known injection device is of complicated design and requires a low-pressure feed pump. Moreover, the injection device does not work effectively enough.
The object on which this invention is based is to provide a liquid gas engine which has a simple design and ensures reliable operation along with a high power output.